Zopiclone a cyclopyrrolone derivative, belonging to a novel chemical class which is structurally unrelated to existing hypnotics chemically named as (±) 6-(5-chloropyridin-2-yl)-7-oxo-6,7-dihydro-5H-pyrrolo[3,4b]pyrazin-5-yl4-methyl piperazine-1-carboxylate of formula (I).

Eszopiclone represented by formula II and is the S-isomer of racemic product Zopiclone. Eszopiclone is found to be more specific for the GABA binding sites and possesses an approximately 50-fold higher binding affinity to GABA-A receptors than the R-Isomer. Also the hypnotic activity of S-Zopiclone is reported to be two folds more than racemic Zopiclone

U.S. Pat. NO. 3,862,149 patent discloses the process for the preparation of Zopiclone, wherein 6-(5-chloropyridin-2-yl)-5-hydroxy-7-oxo-5,6-dihydro pyrrolo-[3,4-b]-pyrazine is condensed with 1-chlorocarbonyl-4-methyl-piperazine in the presence of strong base such as sodium hydride in dimethylformamide to give Zopiclone. According to the prior art process, sodium hydride is used for condensation reaction, handling sodium hydride in the plant level needs lot of safety precautions.
U.S. Pat. No. 6,319,926 patent discloses the process for the preparation of Eszopiclone, wherein (±)-Zopiclone is converted into diastereomeric salts using D(+)-O,O′-dibenzoyltartaric acid in dichloromethane followed by concentration to give crude residue. Crude residue is recrystallised in acetonitrile to obtain solid, which is further subjected to second purification by dissolving in dichloromethane at reflux temperature followed by addition of acetonitrile to give pure salt an over all yield of only 23%.
U.S. Pat. No. 6,339,086 teaches process for the preparation of Eszopiclone, whereas (±)-Zopiclone is converted into diastereomeric salts using D-malic acid in a mixture of acetone and methanol followed by work up to obtain Eszopiclone in an over all yield of 36%.
ES 2,101,653 discloses an enzymatic resolution of racemic mixture of compounds to yield optically pure Eszopiclone.
According to the prior art, processes need repeated crystallization in different solvents to get desired quality of the diastereomeric salt. It leads to yield loss and increase in the raw material cost.
Hence there still exists a need for development of feasible and industrially viable process for synthesis of Zopiclone. The present invention provides the process to prepare therapeutically active enantiomerically enriched isomer of Eszopiclone with improved yield, which is industrially applicable, non-hazardous and less expensive.